The present invention relates to a process and an installation for the recovery and/or purification of the nitrous oxide (N2O) contained in a flow of waste gas, particularly a flow of gas given off by an industrial unit producing adipic acid, nitric acid, glycoxylic acid, nitrous oxide or phenol.
At present, so as to preserve the environment, numerous efforts have been made by industries to put in place systems for treatment of waste, particularly waste gases, such as combustion fumes, which previously were often discharged to the atmosphere without preliminary treatment.
Thus, nitrous oxide is a compound which, in gaseous form, is considered as potentially active in the phenomenon of destruction of the stratospheric ozone layer, given that the latter has a great tendency to decompose to NOx under the influence of natural ultraviolet radiation.
Moreover, nitrous oxide takes part in the greenhouse effect in a manner similar to other regulated gases such as carbon dioxide (CO2) or the fluorocarbonated compounds, such as CFC.
Nitrous oxide is conventionally found in waste gases or off gases discharged to the atmosphere by certain industrial units, such as units for the production of adipic acid or units for the production, purification and storage of nitrous oxide.
As therefore necessary, in order to preserve the environment, to control the quantity of nitrous oxide discharged by this type of industrial unit.
The problem is therefore to be able to recover and, if possible, to recycle or economically use, in an effective manner, the nitrous oxide contained in a waste gas or an off gas and this even if the proportion of nitrous oxide in the waste gas is high, for example more than 20%, even more than 50%.
The present invention therefore relates to a process for the recovery and/or purification of at least a portion of the nitrous oxide (N2O) contained in a flow of waste gas containing nitrous oxide and at least one other gaseous compound, in which:
(a) at least one nitrous oxide portion contained in the flow of waste gas is separated by permeation, and
(b) at least one portion of the gaseous nitrous oxide separated in step (a) is recovered.
Within the scope of the invention, there is meant by xe2x80x9cwaste gasxe2x80x9d, a gas or a gaseous mixture containing nitrous oxide conventionally discharged to the atmosphere with or without preliminary treatment.
As the case may be, the process of the invention can comprise one or several of the following characteristics:
the flow of waste gas to be separated contains from 5 to 99.96 of nitrous oxide, preferably 20 to 99.9% by volume of nitrous oxide, more preferably 50 to 99.9% of nitrous oxide, by volume;
the flow of waste gas to be separated contains, in addition, at least one gaseous compound selected from the group consisting of nitrogen, oxygen, carbon monoxide and gaseous compounds having a speed of permeation different from that of N2O;
the permeation is carried out by passage of the flow of waste gas to be separated through at least one permeation module, preferably at least one module with membrane fibers;
the permeation is carried out by passage of the flow of waste gas to be separated through several permeation modules, preferably with membrane fibers and/or arranged in cascade;
in step (b), a gas is recovered containing 80% to 100% of nitrous oxide, preferably at least 90% of nitrous oxide, more preferably at least 95% of nitrous oxide;
the flow of waste gas to be separated is an off gas from an industrial process, preferably an off gas from a process for the production of adipic acid, a process for the production of nitrous oxide, a process for the production of phenol, a process for the production of nitric acid or a process for the production of glycoxylic acid;
the waste gas to be separated is at a temperature comprised between xe2x88x9230xc2x0 C. and +80xc2x0 C., preferably xe2x88x9220xc2x0 C. to +60xc2x0 C.;
the waste gas is at a pressure of 105 Pa to 107 Pa, preferably 106 Pa to 6.106 Pa;
in step (b), a gas containing principally nitrous oxide is recovered at the permeate outlet of at least one permeation module;
in step (b), a gas containing principally nitrous oxide is recovered at the retentate outlet of at least one module.
The invention also relates to an industrial installation adapted to use the process of the invention, which industrial installation permits the recovery and/or purification of at least one portion of the nitrous oxide contained in a flow of waste gas containing nitrous oxide and at least one other gaseous compound, said installation comprising:
at least one source of a flow of waste gas containing nitrous oxide and at least one other gaseous compound,
permeation means permitting separating by permeation at least one portion of the nitrous oxide contained in the flow of waste gas, and
means for recovering at least one portion of the nitrous oxide separated by the permeation means.
As the case may be, the installation can comprise one or several of the following characteristics:
the source of the flow of waste gas is an industrial unit using an industrial process discharging waste gas, preferably a unit for the production of adipic acid, a unit for the production of nitrous oxide or a unit for the production of phenol, a unit for the production of glycoxylic acid or a unit for the production of nitric acid;
the permeation means comprise one or several membrane modules.